DC power supplies incorporated in magnetic disk memories have been for the most part standardized at +5 and +12 volts. Thus, typically no provision is made for an onboard negative voltage source despite the frequent need therefor to power integrated circuit devices such as analog-to-digital converters, random access memories and operational amplifiers calling for bipolar supply voltages. Where negative voltages are required, switching power supplies external to the disk memory device are usually employed to convert an existing positive voltage. However, such supplies require components such as choppers, transformers and rectifiers as well as filter and regulator stages which tend to be both bulky and expensive. Moreover, they often generate electrical noise which can interfere with the operation of other components and adversely affect the data transfer function of the disk memory.